October 1937 Radio-Craft
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Instrument Landing System (ILS) has been around for an amazingly long time -
almost as long as commercial airlines have been operating. This 1937 article in
the October issue of Radio-Craft magazine reports on the current state
of the art. The Douglas DC-3 twin-engine airliner (my all-time favorite airplane)
entered service in 1936 and is credited with creating widespread public acceptance
of the safety and comfort of airplanes. Much of the content for this article also
appeared in "The History and Development of the Washington Institute of Technology,"
by Joseph M. Mahzolf, Jr., published November 18, 1938. The ILS has been replaced
or augmented in many locations with the
Landing System (MLS) and/or the GPS-based
Wide Area Augmentation System (WAAS).
"Air-Track" System of Blind Landing
By Charles E. Planck
Fig. a - Note "cross-pointer" (course indicator) meter on
The familiar "curved beam" radio safe landing system has been developed by the
Washington Institute of Technology to the point where it is now ready for commercial
use on any airport. Figure A is an action view of the system shown in Fig. B.
(Figure B is a phantom diagram prepared by staff artist T. D. Pentz.)
Six important improvements have been incorporated in the Air-Track. Foremost
among these are the facts that (1) the equipment has been so simplified and the
design made so compact, that it is portable, making it possible to lead a pilot
in to a safe landing from either end of any runway on the field; (2) the radio signals,
at first liable to deviation and instability, have been made reliable, and a monitoring
system installed which indicates to the operator whether accurate signals are being
broadcast; (3) both the localizer and the glide path are quickly adjustable and,
(4) the equipment required in the plane has been made lighter and more efficient.
The principles embodied in this system were originally worked out by an Aeronautics
Research Division established by the Department of Commerce at the Bureau of Standards.
A number of the radio scientists who developed the system at the Bureau have been
at work in a laboratory at College Park Airport near Washington developing the system
from its early experimental stages to the point where it is now practical for air
transport. Three years of such development and improvement work have resulted in
hundreds of successful landings "under the hood" and landings in fog conditions
which interrupted scheduled flying.
Three experimental installations of this curved beam type of landing system have
been tested by Department of Commerce pilots, airline pilots and others. These are
at College Park, Newark airport, and the municipal airport at Oakland, California.
In all, upwards of 1,000 safe instrument landings have been made on these installations.
Fig. B. Any deviation of the plane from the sloping "air
track" while landing is instantly recorded on the "cross-pointer" meter on instrument
Elements of the Air-Track System
Briefly, the Air-Track system consists of two radio beams: (1) a runway localizer
which lies down the center of the runway to be used. and (2) a curved glide path
which leads the plane down a loping "track" to a gentle landing on the runway. A
single "cross-pointer" instrument (2 D.C. meter movements, one operating horizontally
and the other vertically, mounted in one case) on the panel (see Fig. A) indicates
the plane's position, the vertical needle pointing to the right or left if the plane
veers from the center of the runway localizer, and the horizontal needle rising
or falling if the plane gets above or below the proper glide path.
At a distance of 10 or 15 miles from the airport (see Fig. B), the pilot
picks up the runway localizer signal through his regular communications receiver,
over which he still receives voice communication, perhaps from the operator in the
airport control tower. Lining up his flight along this localizer, which can be made
as wide or as narrow as comfortable flying dictates, he approaches the curved beam
down which he will glide to the runway. (The receiver for this glide path is adjusted
to the best "gliding angle" of that type of plane.)
Having reached this point, the pilot flies his plane so that the 2 needles cross
at right-angles, and this indicates that he is approaching over the exact center
of the runway and coming down at the proper safe gliding angle.
At the edge of the field a marker beacon gives him a signal in his earphones
which tells him he is crossing the edge of the field. At this time he is approximately
20 to 30 feet above the runway, and the balance of the landing consists merely of
leveling off and letting the plane settle.
Hundreds of times, planes with landing speeds as high as 75 miles an hour have
been brought down to a spot on the field a few yards square! James L. Kinney, Department
of Commerce pilot, as far back as 1933, took off from Washington under the hood
(that is, he could not see outside the plane, had only his instruments to guide
him, and hence was flying "blind"), flew by instrument to Newark airport, and landed
by instrument on the experimental installation of this system, on a day when scheduled
air transport planes were grounded by impossible flying weather.
Transmitting equipment is housed in an ordinary automobile trailer which is quickly
movable to concrete platforms at either end of any runway, where the wheels fit
into slots to insure proper location of the apparatus. The transmitters are plugged
in to a power outlet and the control tower attendant throws a switch which puts
them into operation.
Usefulness of "Air-Track" at Crowded Airports
Usefulness of the apparatus for control of traffic at crowded airports has been
stressed by pilots who have flown the system. Airline officials have pointed out
that if all landings of air transport planes were made on this system, even in fine
weather, a pilot would never make an unusual landing, no matter what the weather
Despite the thoughtful and serious work of airline operations managers and traffic
managers in "staggering" schedules to avoid simultaneous arrival of several airliners
at one airport at the same time, the airports at large municipalities are already
dangerously crowded at certain times. At one airport today, there are 18 transport
planes arriving within the space of an hour. Increasing patronage will only aggravate
this problem, and bad weather complicates it to the point of deadly hazard.
It is as if the engineers of a large number of trains were instructed to choose
their own track and bring their trains in to a huge station with only the admonition
to "be careful and not run into other trains." The airline pilot has two-way voice
communication with the airport control tower, and receives all the information available,
but he does not have a definite "track" or path to follow which will keep him clear
of other approaching aircraft.
A correct blind landing system may have a number of duplicate "tracks", properly
identified, just as are the tracks in a railroad yard, and the approaching pilot's
orders will indicate the track he is to use. Eventually, these engineers believe,
the "switches" may be set for the approaching pilot, and his plane may be taken
over by radio when he is distant from the field, and brought in mechanically to
a full instrument landing. This dream is not very nebulous, even today.
Comparison of Various Blind-Landing Systems
There are no "preceding types" of landing systems prior to the Air-Track. It
is based definitely upon the original experiments at the Bureau of Standards, which
began in 1927 and 1928. An Aeronautical Development Section of the Department of
Commerce, Aeronautics Branch, conducted those experiments, and carried them up through
various stages of development to the demonstrations held at Newark in 1933.
As for other landing systems (Most of these systems have been described in past
issues of Radio-Craft. -Editor), this is the story. In 1931 or 1932, visitors from
Germany were shown the Bureau's developments and after their return to Germany the
Lorenz system appeared. This is a refinement and development of one of the phases
of the Bureau development.
At Newark, the Bureau installation was fixed in position, giving indication in
only one direction. The Lorenz system today is also fixed in one position. If it
is desired to give landing guidance on more than one runway, or in more than one
direction, the installation must be duplicated. This means that under certain conditions,
the pilot will be coming in to land over the antenna structure and transmitter houses.
These form a positive obstacle, much disliked by pilots. There is also the consideration
of the added expense necessary to duplicate these transmitters and antenna arrays
The Lorenz system also uses a European type of indication, with a kicking needle
indicating off-course position. This is strange to American pilot practice and preference,
and it requires an appreciable time for interpretation. There is no time available
for interpretation in the job of blind landing.
The Lorenz system holds to the fundamental principles of the Bureau system, i.e.
the "curved beam", localizer and marker beacons. It gives the pilot an indication
of his position throughout the approach and landing. However, it is not all contained
on the airport, and it has not been developed as far as Air-Track.
The success of the Bureau demonstrations at Newark prompted the duplication of
the system at Oakland airport in California. Here, United Airlines, later joined
by TWA and American Airlines, and still later by Bendix, have continued their development.
They have not released much on their development, but we understand that it is still
fixed in position, although it retains the fundamental principles of the Bureau
The 4 major Airlines, AA, TWA, UAL and EAL, meeting with Bureau of Commerce and
Federal Communications Commission representatives recently set forth: recommended
specifications for instrument landing to be adopted on a national scale.
It is interesting to note that Air-Track exceeds the operating requirements of
these specifications, meets all the requirements described as "practicable," and
most of those which are called "projected developments." For example, the specifications
suggest that glide path and localizer indications should be separate. The Bureau
started with separate transmitters and we regard them as essential to safety and
We believe this instrument landing situation has implications which make it the
biggest story in radio or aviation at this time. Entirely aside from the safety
angle, its economic angle is sure to have a tremendous effect on the history of
When a curtailment of funds necessitated a discontinuance of Department of Commerce
activities on radio aids to flying in 1933, scientists who had been employed at
the Bureau were set up in a new laboratory at College Park where they continued
their research and experiments.
Among these men were Gomer L. Davies, Dr. Frank G. Kear, Gerald H. Wintermute,
and the late William H. Orton, who are largely responsible for the improvement of
the Air-Track and its adaptation to commercial needs.
The first job of instrument landing is to save lives. Its second job is to make
possible the completion of every trip interrupted or cancelled because the terminal
airport is "closed in", and thus to guarantee flying on an announced schedule. The
story of its contributions will be the first chapter in an entirely new epoch of
Airlines of the country took a big step toward 100% in safety and regularity
of scheduled operation when they recently agreed upon specifications for an acceptable
instrument landing system.
As a result, it appears that a workable system will have been tested and accepted
before the arrival of bad flying weather this winter.
Posted October 7, 2016